1. Field of the Invention
This invention relates to the field of electro-inductive devices, such as electrical transformers. More specifically, this invention relates to an assembly for monitoring the temperature within a winding of such a device, and a method for making such an assembly.
2. Description of the Prior Art
An electrical transformer 10 such as that which is depicted in FIGS. 1 and 2 typically includes a ferrous core 12 about which a number of windings 14 are wound. As is shown in FIG. 1, a number of leads 16 are electrically connected to windings 14, in a manner that is well known to those in the industry. One type of winding 14, as shown in FIG. 2, is fabricated from a strip conductor 18, upon which insulation 20 has been deposited. A number of cooling ducts 22 are formed between adjacent layers of insulation 20 by means of a plurality of duct sticks 24 which are interposed between the adjacent layers. During normal operation, electrical transformer 10 is typically suspended in a liquid, which fills ducts 22 and provides a cooling effect to the windings 14.
In many applications, it is desirable to monitor or measure the temperature within one or more of the ducts 22 in winding 14. One way to accomplish this would be to use a standard thermocouple which is inserted into the duct 22. However, because a thermocouple is electrical in nature it might be dangerous or otherwise disadvantageous for use within an electrical transformer 10.
It is known that an optical fiber may be used to measure temperature. In one known technique, a short pulse of light, typically several nanoseconds in length and at an appropriate wavelength, is launched into one end of the fiber. As the pulse of light propagates along the fiber, it is scattered by a variety of reasons in all directions. A proportion of this scattered light makes its way back to the same end of the fiber into which the light was launched. By using some form of directional coupling of the light, this back scattered light is optically detected. The total spectrum of received back scattered radiation is dominated by Rayleigh scattering, which is not particularly sensitive to temperature. However, certain components of the scattered spectrum are sufficiently sensitive to temperature (in particular the so-called Raman spectrum) so as to provide a convenient mechanism for its measurement. One such system which is commercially available is the York Distributed Temperature Sensor System that is commercially from York Technology of Hampshire, England.
Fiber optic filament temperature sensing systems are well suited to measuring the temperature in inductive devices, because of their non-electrical nature. However, the resolution such equipment presently requires at least 7 meters of filament length. Optical fibers are relatively fragile, and are difficult to fit into a duct 22 without adversely applying mechanical stresses which could damage the filament.
It is clear that there has existed a long and unfilled need in the prior for an improved system and method which permits an optical fiber temperature measurement system to be used for measuring the internal temperature of an electro-inductive apparatus without adversely applying mechanical stresses to the optical fiber during deployment and operation.